Known pneumatic feeders, as distinguished from mechanical feeders, are inexpensive and relatively easy to install in a production operation as they have no mechanical drive connection to a downstream machine such as a power press and the like and are accurate since the cycle of the actuating feed device is conventionally limited by positive mechanical stops at each end of the feed stroke.
However, a significant limitation of such known pneumatic feeders is the cycle rate at which they are capable of operating. In general, they must complete two strokes, the idle return stroke and the forward feed stroke, in limited allowed time periods.
Recent contributions to the art feature two conventional feed devices, one behind the other in tandem relation. One feed device returns as the other feed device feeds the stock to the downstream machine. This action considerably increases the cycle rate but also results in a rather elongated structure and has presented undesirable buckling problems when used with thin stock material.
A high speed dual-slide type pneumatic feeder is also disclosed in U.S. Pat. No. 4,051,987 issued in the name of Robert W. Scribner which is also an improvement in the pneumatic feeder art in intermittently advancing strip stock into a downstream work station whereby alternately acting feed slides are operable for strip stock advancing movements with one of the feed slides being activated to perform a stock advancing function during a simultaneous idle return stroke of the other feed slide.
However, a basic and heretofore unsolved problem inherent in the use of any known pneumatic feeder is the seemingly incompatible resolution of achieving precision stock positioning at the termination of an advancing feed stroke of the material at extraordinarily high feed rates and at the same time terminating that feed stroke to zero velocity in a non-destructive fashion. In addition, it is desired to both ensure termination of movement of the feed stroke and the feeder components while simultaneously ensuring against slippage of the stock material in a forwardly advancing direction upon arresting the feed component movement.
Simply stated, there are significant problems presented in attempting to achieve high production rates and yet bringing the mass of the feed mechanisms and stock material to zero velocity suddenly in production runs frequently requiring a magnitude of 300 strokes or more per minute with each stroke providing about a 4 inch advance. Previous attempts have been made to utilize trapped exhaust air in power drive cylinders to serve as buffers. This approach has been found to create undesired lengthening of the feeder cycling time. Insufficient buffering to increase the feed rate has proven to be ultimately destructive on positive mechanical stops, which are commonly utilized in the conventional art, and undesirably causes an excessive noise level and eventual loss of accuracy in the stock feed.